(* pgm1-Date.cl - 
Kishen Maloor
CIS, University of Delaware.

This is an object oriented program which calculates the day 
for an entered date that is after January 1st, 1980, and 
displays it as the output to the user.

The "Date" class contains the procedure that carries out
this function. The use of the individual attributes and 
other secondary variables in this class have been defined.

The main idea behind this implementation is to 
first calculate the total number of days between the 
entered date and the 1st of January, 1980.
This number is divided by 7 to determine the number of
weeks that the period corresponds to. The remainder
after division would give us the # of extra days to be
counted after the day that corresponds to the 1st of
January, 1980 to reach the exact day for the entered date.
This result is displayed for the user. *)

-- the Date class

class Date inherits IO {

d : Int;  -- entered date
m : Int;  -- entered month
y : Int;  -- entered year
yd : Int; -- number of yrs in between y and 1980
c : Int;  -- counter
nduly : Int; -- number of days in between entered date and 111980
nw : Int;  -- number of weeks between 111980 and dmy
lw : Int;  -- number of extra days in the last week
fstd : Int;  -- day that corresponds to 111980
leap : Int;  -- leap year count
m1 : Int <- 1; -- months 1 to 12
m2 : Int <- 2;
m3 : Int <- 3;
m4 : Int <- 4;
m5 : Int <- 5;
m6 : Int <- 6;
m7 : Int <- 7;
m8 : Int <- 8;
m9 : Int <- 9;
m10 : Int <- 10;
m11 : Int <- 11;
m12 : Int <- 12;

-- for initializing the Date class
init(dd : Int,mm : Int,yy : Int) : Date {
 {
  d <- dd;
  m <- mm;
  y <- yy;
  self;
 }
}; 

-- for calculating the number of days in between dmy and 111980

noduly() : Int {
 { 
  c <- 1980;
  yd <- y - c;
  nduly <- 0;
  leap <- 4;
  while c <= (y-1) loop {
   if leap = 4 then
   {
    nduly <- nduly + 1;
   }
   else if leap = 0 then
   {
    nduly <- nduly + 1;
    leap <- 4;
   }
   else
   {
    nduly <- nduly + 0;
   }
   fi fi;
   leap <- leap - 1;
   nduly <- nduly + 365;
   c <- c+1;
   } pool;
   
   if leap = 4 then {
     if 2 < m then {
     nduly <- nduly + 1;}
     else { nduly <- nduly+0;}
     fi; }
   else if leap = 0 then {
     if 2 < m then {
     nduly <- nduly + 1;}
     else { nduly <- nduly+0;}
     fi; }
   else {
     nduly <- nduly + 0; }
   fi fi;
  
   c <- 1;  -- counter

   while c <= (m-1) loop {
   if c = m1 then { nduly <- nduly + 31; }
   else if c = m2 then { nduly <- nduly + 28; }
   else if c = m3 then { nduly <- nduly + 31; }
   else if c = m4 then { nduly <- nduly + 30; }
   else if c = m5 then { nduly <- nduly + 31; }
   else if c = m6 then { nduly <- nduly + 30; }
   else if c = m7 then { nduly <- nduly + 31; }
   else if c = m8 then { nduly <- nduly + 31; }
   else if c = m9 then { nduly <- nduly + 30; }
   else if c = m10 then { nduly <- nduly + 31; }
   else if c = m11 then { nduly <- nduly + 30; }
   else { nduly <- nduly + 31; }
   fi fi fi fi fi fi fi fi fi fi fi;  
   c <- c+1;
   } pool; 

  nduly <- nduly+d;  
  nduly;
 }   
};

-- to determine and display the actual day

actdat() : SELF_TYPE {
{
 fstd <- 2;
 nw <- nduly / 7;
 nw <- nw*7;
 lw <- nduly - nw;
 fstd <- fstd + lw;
 if fstd <= 7 then {
  fstd <- fstd + 0; }
 else {
  fstd <- fstd - 7; }
 fi;
 if fstd=1 then { out_string("Sunday"); }
 else if fstd=2 then { out_string("Monday"); }
 else if fstd=3 then { out_string("Tuesday"); }
 else if fstd=4 then { out_string("Wednesday"); }
 else if fstd=5 then { out_string("Thursday"); }
 else if fstd=6 then { out_string("Friday"); }
 else { out_string("Saturday"); }
 fi fi fi fi fi fi; 
}
};

-- higher level routine that calls lower level routines to perform the subtasks

compute() : SELF_TYPE {
 {
  noduly();
  actdat();
 }
};

};

-- the main class

class Main inherits IO {

-- variables to hold the input date

d : Int;
m : Int;
y : Int;

obj : Date;  -- for the object of the Date class

-- main function

main() : Object {
 {
 out_string("Enter any date on or after 1st Jan, 1980.\nThe  corresponding day will be displayed.\n");
 out_string("dd : ");
 d <- in_int();
 out_string("mm : ");
 m <- in_int();
 out_string("yyyy : ");
 y <- in_int();
 obj <- new Date;
 obj.init(d,m,y);
 obj.compute();
 }
};

};